The present invention relates to fuel injection systems, and pertains more particularly to an injection valve assembly for an internal combustion engine.
Compression ignition engines commonly employ fuel injection nozzles for delivering a timed injection of fuel into the engine combustion chamber. Such nozzles are normally controlled by a pressure-responsive check valve to prevent dribbling of fuel into the combustion chamber between injection strokes. Numerous types of different check valve arrangements have been used in such nozzles; however, each arrangement has been found to have certain disadvantages.
A simple outwardly opening check valve is exemplified by U.S. Pat. No. 2,410,946, issued Nov. 12, 1946 to Lloyd E. Johnson which requires no close tolerances or lap fits. However, its principal disadvantage is the relatively large volume between the check seat and combustion chamber. This volume has a deleterious effect on control of injection and may tend to dribble fuel into the cylinder.
One preferred type of fuel nozzle, because of its operational simplicity, is the differential area type check valve as exemplified by U.S. Pat. No. 2,379,399, issued June 26, 1945 to H. F. Haines, U.S. Pat. No. 2,865,675, issued Dec. 23, 1958 to V. D. Roosa, and U.S. Pat. No. 3,224,684, issued Dec. 21, 1965 to V. D. Roosa. The major problem with these types of fuel nozzle and valve arrangements is that they must employ a low-pressure chamber into which the valve stem must extend in order to provide a low pressure in opposition to the actuating pressure to provide the necessary pressure difference for actuation of the valve. Such valve arrangements result in leakage around the valve stem to the low-pressure chamber, resulting in the need to provide leak off manifolds and the like.
The aforementioned differential area valves also normally employ a rather large compression spring to close the valve. When the spring is located near the fuel orifice, it increases the diameter of the injector valve assembly and the size of bore in the cylinder head required to accommodate it. When the spring is located remote from the fuel orifice, the alignment of the check valve needle becomes more critical.
Other examples of the known prior art are: U.S. Pat. Nos. 3,451,626 issued June 24, 1969 to Roosa; and 3,598,314 issued Aug. 10, 1971 to John M. Bailey et al, and 3,750,960 issued Aug. 7, 1973 to John H. Back et al, both of common assignment herewith.
These valves are selfcentering; however, they have a disadvantage of having the relatively large diameter spring close to the orifices which tends to complicate installation. Also, unlike conventional inwardly opening valves, the spring is located in the higher pressure inlet passage wherein the rather large volume required may adversely affect performance.